Definition

VoLTE (Voice over LTE) is a technology that delivers voice calls over the 4G LTE data network using IMS (IP Multimedia Subsystem). It replaces circuit-switched voice with packet-switched IP-based voice, offering HD voice quality and faster call setup times.

Glossary

What is VoLTE?

Q: What is VoLTE and how does it work?

VoLTE (Voice over LTE) delivers voice calls over the 4G LTE data network using IMS (IP Multimedia Subsystem) instead of falling back to 2G/3G circuit-switched networks. Voice is encoded as IP packets using AMR-WB or EVS codecs and carried over dedicated QCI 1 bearers with guaranteed quality of service.

Q: What is the difference between VoLTE and VoNR?

VoLTE carries voice over 4G LTE using IMS, while VoNR (Voice over New Radio) carries voice over 5G NR using the same IMS framework. VoNR offers lower latency and better integration with 5G features like network slicing. During the transition, EPS Fallback allows 5G devices to use VoLTE for voice calls.

Q: How is VoLTE call quality measured?

VoLTE call quality is measured using MOS (Mean Opinion Score) derived from objective algorithms like POLQA or PESQ. Additional KPIs include call setup time, call drop rate, RTP jitter, packet loss and codec negotiation. HiCellTek measures VoLTE QoE KPIs in real time during field testing.

Voice over LTE: HD voice calls delivered natively over the 4G data network.

Detailed explanation

VoLTE uses the IMS (IP Multimedia Subsystem) architecture to establish and manage voice calls entirely within the LTE packet-switched domain. When a VoLTE call is initiated, the network establishes a dedicated EPS bearer with QCI 1 (conversational voice) that guarantees low latency and prioritized treatment throughout the call duration.

The voice signal is digitized using wideband codecs such as AMR-WB (Adaptive Multi-Rate Wideband) or EVS (Enhanced Voice Services). These codecs sample audio at 16 kHz or higher, delivering HD voice quality that is noticeably superior to traditional narrowband calls. The encoded voice is packetized into RTP/UDP/IP packets for transport over the LTE bearer.

VoLTE offers several advantages over legacy circuit-switched voice: faster call setup (under 2 seconds vs 5 to 7 seconds), simultaneous voice and high-speed data, spectrum efficiency (no need to maintain 2G/3G for voice) and support for enriched services like video calling and Wi-Fi calling through the same IMS platform.

Quality of Experience (QoE) monitoring for VoLTE involves measuring MOS (Mean Opinion Score), call setup success rate, call drop rate, handover success during calls, RTP jitter and packet loss. These KPIs are essential for operators to ensure VoLTE delivers consistent quality across their network coverage area.

VoLTE quality metrics

KPI	Target	Impact
MOS	≥ 3.5	Perceived voice quality
Call Setup Time	< 3 s	User experience
Drop Rate	< 1 %	Service reliability
RTP Jitter	< 30 ms	Voice clarity

How HiCellTek measures VoLTE

The VoLTE QoE module in HiCellTek monitors all VoLTE call quality metrics in real time: MOS score, call setup time, RTP statistics, codec negotiation and SIP signalling. Combined with the RF Monitor, it correlates voice quality degradation with radio conditions to pinpoint root causes of poor VoLTE performance.

Frequently asked questions

What is VoLTE and how does it work?

VoLTE (Voice over LTE) delivers voice calls over the 4G LTE data network using IMS (IP Multimedia Subsystem) instead of falling back to 2G/3G circuit-switched networks. Voice is encoded as IP packets using AMR-WB or EVS codecs and carried over dedicated QCI 1 bearers with guaranteed quality of service.

What is the difference between VoLTE and VoNR?

VoLTE carries voice over 4G LTE using IMS, while VoNR (Voice over New Radio) carries voice over 5G NR using the same IMS framework. VoNR offers lower latency and better integration with 5G features like network slicing. During the transition, EPS Fallback allows 5G devices to use VoLTE for voice calls.

How is VoLTE call quality measured?